Medical devices may be implanted into human bodies to treat diseases. For example, heart pacemakers are implanted to treat an irregular heartbeat. In general, such pacemakers incorporate a battery for driving a control device and send electric pulses controlled by the control device to the heart muscle via lead wires. However, they need to be replaced before the battery runs down. To replace the battery, the pacemaker need to be removed from the patient body, which is a heavy burden to the patient. In view of this, pacemakers have been developed that incorporate a rechargeable secondary battery that can be charged from outside the human body with the pacemaker kept implanted therein.
For example, JP-3743152-B discloses an electronic device for use in a living body that can be applied to pacemakers etc. This electronic device is equipped with a large gear to which a magnet is fixed, a generator having a small gear which is in mesh with the large gear, a rectification circuit, and a rechargeable secondary battery. A magnetic field generation device having a coil that is connected to an AC power source is set outside a human body. A rotary magnetic field generated by the magnetic field generation device causes rotation of the magnet and hence rotation of the large gear in the electronic device. The small gear is rotated resultantly and causes the generator to generate power, which charges the secondary battery via the rectification circuit.
Whereas the above electronic device for use in a living body incorporates the mechanical power generation structure including the large and small gears, devices are also known that employ a wireless power supply method in which power is supplied from outside a human body through electromagnetic induction. JP-2009-529975-A discloses, as an example device of the latter type, a pacemaker having a wire loop inside and a rechargeable inner battery. A charger for charging the internal battery from outside the human body has a hollow, disc-shaped capsule. Plural rotatable wire loops extend adjacent to the inner wall of the capsule. Referring to FIG. 1 of JP-2009-529975-A, the wire loops in the charger are wound so as to be large enough to be able to be located outside a control device and lead wires provided inside the pacemaker. The charger is brought into contact with a human body surface adjacent to which the pacemaker is implanted and an AC current is caused to flow through the wire loops of the charger. A magnetic flux is generated by the wire loops, whereby a current is induced in the wire loop of the pacemaker and its internal battery is charged.
In the electronic device for use in a living body that is disclosed in JP-3743152-B, if the coil of the magnetic field generation device disposed outside the human body generates an excessively strong magnetic field for the generator of the implanted electronic device to generate sufficient power, a control device, lead wires, etc. of a pacemaker may suffer an adverse effect such as an erroneous operation. Furthermore incorporating the mechanical power generation structure including the large and small gears, the electronic device cannot easily be made compact.
In the pacemaker disclosed in JP-2009-529975-A, since the wire loops of the charger are disposed outside the control device and the lead wires of the pacemaker, a magnetic flux generated by the wire loops of the charger crosses not only the wire loop provided inside the pacemaker but also its control device and lead wires to cause an erroneous operation or the like there.